In case you don't understand.
This is a SUBJECTIVE marker for when a decision was made.
And many subjects press the button BEFORE the alleged autonomous "brain decision".
You miss the point. There are two points of interest here, one being when the subject experiences making a conscious decision and pressing the button. The second and most important point, the unconscious information processing activity leading up to the conscious experience of decision making. The evidence supporting that the latter determines the former. In other words, that unconscious information activity prior to conscious experience shapes and forms conscious experience.
That is what you do your utmost best to deny and avoid in order to maintain your unfounded, untenable notion of autonomy of consciousness. You have no evidence, you have no argument, you have no case to argue. It would be better for you if you just conceded gracefully.